Known in the art are hoses comprising an inner tube, a reinforcing layer, and an outer cover laminated on each other annularly in that order. In these hoses, the inner tube and outer cover are comprising a vulcanized rubber, or resin such as urethane, polyester, nylon, the reinforcing layer is composed of a fiber such as nylon, polyester, rayon, vinylon, aramide fiber, braided or spiralled, and the layers are treated to be bonded with each other using a rubber cement, urethane adhesive, etc.
However, a so-called "rubber hose" using rubber for the inner tubes and outer covers requires a vulcanization step, and therefore the manufacturing process ends up becoming complicated. Further, a so-called "plastic hose" using just a thermoplastic resin for the inner tubes and outer covers has the problem that the hose is rigid and poor in flexibility and kinks when the hose is bent.
As a proposal to solve the above problem, there has been proposed a hose using a thermoplastic elastomer composition comprising a thermoplastic resin such as a polyolefin thermoplastic resin, a polyvinyl chloride thermoplastic resin, a polyamide thermoplastic resin, a polyester thermoplastic resin, in which an at least partially cross-linked vulcanized rubber phase is dispersed (see for example Japanese Unexamined Patent Publication (Kokai) No. 6-64102).
However, from the viewpoint of an oil resistant hose, since a general polyolefin thermoplastic elastomer composition comprises a polypropylene and an ethylene-propylene rubber and has no polar group in its molecular structure, it has the defect of being poor in oil resistance. On the other hand, to improve the oil resistance, thermoplastic elastomers comprises polypropylenes and acrylonitrile-butadiene rubbers and thermoplastic elastomers comprises ethylene-acrylic ester copolymer rubbers and polyolefins have been proposed, but while the former are superior in oil resistance, they have double bonds in the molecular structure, and therefore, have the defects of inferior heat resistance and weatherability, while the latter are superior in heat resistance and weatherability, but have ethylene portions in the molecular structure of the rubber, and therefore, have the defect of a continued insufficient oil resistance.
To solve these problems, various studies have been made on thermoplastic elastomers comprising acrylic rubbers and polyolefin resins superior in oil resistance and heat resistance, but there is the problem that they lack compatibility.
Japanese Unexamined Patent Publication (Kokai) No. 6-136190 discloses a thermoplastic elastomer comprising a thermoplastic polyolefin resin and an acrylic ester containing a nonconjugated diene. A polyolefin resin and acrylic rubber are inherently incompatible, but no compatibilizer is used for the thermoplastic elastomer. It is considered that an excess amount of peroxide acts on the polyolefin as well causing the production of a polyolefin having radicals and that these radicals and the nonconjugated diene portions of the acrylic rubber react and produce graft polymers of the two.
Japanese Unexamined Patent Publication (Kokai) No. 7-149964 discloses a thermoplastic elastomer comprising an ethylene-acrylic ester copolymer rubber and an olefin copolymer. No compatibilizer is used for this thermoplastic elastomer as well. The ethylene sites are merely partially cross-linked. The compatibility is unknown. Further, the ethylene-acrylic ester copolymer rubber used here does not have an epoxy group.
Japanese Unexamined Patent Publication (Kokai) No. 62-290741 discloses a thermoplastic elastomer comprising a polyolefin resin and an ethylene-acrylic ester copolymer rubber having an epoxy group. An embodiment using a compatibilizer is also disclosed, but in this thermoplastic elastomer, the epoxy groups are used as cross-linking sites.
On the other hand, a plastic hose comprising an inner tube, a reinforcing layer, and an outer covering layer laminated with each other annularly in that order, using a resin such as a nylon, polyester elastomer, polyacetal, urethane, for the inner tube, using a zinc-plated hard steel wire etc. for the reinforcing layer, and interposing a polyolefin resin layer having a functional group between the layers is disclosed in Japanese Unexamined Patent Publication (Kokai) No. 55-97948. Further, steel wire treated on its surface with a triazine thiol derivative to improve its corrosion resistance and bondability with rubber is disclosed in Japanese Examined Patent Publication (Kokoku) No. 7-122225. However, until now, no example has been known of use of these techniques for a thermoplastic elastomer composition comprising a thermoplastic resin in which is dispersed a cross-linked elastomer.
On the other hand, a process for the production of a wire-reinforced plastic hose having two wire reinforcing layers sandwiching a bonding use sheet coated with an epoxy resin etc. or a synthetic resin sheet between the hose inner layer and outer covering where after the wires are covered, induction heating is applied to bond the wires and bonding use sheet and outer covering is disclosed in Japanese Unexamined Patent Publication (Kokai) No. 54-159468.
These related art relate to hoses using a nylon, polyester, polyurethane, or other resin for the inner tube and outer cover and to processes of production of such plastic hoses. Hoses using a nylon, polyester, polyurethane, or the like, however, were not sufficient in flexibility or durability.
Until now, no wire-reinforced hose using a thermoplastic elastomer composition comprising a thermoplastic resin in which is dispersed a cross-linked elastomer was known. Development of a wire-reinforced hose using a thermoplastic resin flexible and superior in durability has therefore been desired.